void oval2(double xf, double yf) 
{  

while(yf <= 0) { 
                     // simply bruteforce...

     forma= sqrt((xf-13)/a) + sqrt((yf-2)/b);
     
      yf++;
      if (forma>=1) //if point is right then add this in the table
      {
                    yf=3;
    x[4]=xf;
    y[4]=yf;
    break;
}
          
}

oval2(0,-40);